1. Field of the Invention
This invention relates to a thermos bottle and, more particularly, to a stainless steel thermos bottle with excellent thermal insulating properties.
2. Description of the Prior Art
Thermos bottles which are now widely used are usually made of glass and are of a double-walled construction, with a vacuum in the space between the two walls. Such glass thermos bottles have the advantages of high heat insulating properties, but are poor in resistance to mechanical shocks. Thus, if any mechanical shock is given, breakage of the bottles and effluence of their contents can result. As thermos bottles with high resistance to mechanical shocks there have recently been proposed metal thermos bottles, which are made of a suitable metal material such as stainless steel, some of which have been put into practical use. For example, there is a metal thermos bottle which is made of stainless steel and is of a vacuum insulated, double-walled construction. In order to decrease the heat transfer due to radiation the inner bottle is polished and a composite material is arranged in the vacuum space formed between inner and outer bottles. The composite material generally comprises one or more lustered thin steel or aluminium plates and glass wool layers. In an alternative form the vacuum space is packed with a large amount of a mixture comprising fine-grained powder of graphite, diatom earth and calcium oxide.
These metal thermos bottles have the advantages of high resistance to mechanical shocks, and their outer bottle per se can serves as an outer jacket. However, these metal thermos bottles are considerably inferior to the glass thermos bottles in thermal insulating properties, which are the most important properties of thermos bottles. This problem mainly depends on the physical properties of the metal used and the construction of the thermos bottle. Particularly, the metal material contains some gases such as hydrogen, so that the gas would be liberated from the interior of the metal into the vacuum space, with the result that the vacuum becomes progressively worse with time. Thus, it is difficult with such a metal thermos bottle to maintain the thermal insulating properties for a long time. In the prior art metal thermos bottles it has been attempted to prevent the lowering of the vacuum by use of a getter material with which the gas released from the metal into the vacuum space combines to form stable compounds. However, there is no prior art metal thermos bottle with thermal insulating properties which are as good as glass thermos bottles.